Windows XP , have many problems with graphic - games.
try to update your graphic card, or change your resolution.
1. Press : + R
2. write regedit.
3. Click to"" Software "" Valve , Half-life , click to Settings.
4. search , Screen Height And Screen Width .
5. Click to Screen Height And Modify. put 600.
6. Click to Screen Width And Modify. put 800.
7. Open your Counter strike 1.6.
P:S. when you go to change a value, put decimal.
I hope help you ,Have a nice day.